The following publications are illustrative of the most relevant prior art known to the applicant at the time of filing this application:
______________________________________ U.S. Pat. Nos. ______________________________________ 2,216,135 Rainier Oct. 1, 1940 2,308,982 Kistler Jan. 19, 1943 2,811,430 Gregor et al Oct. 29, 1957 2,939,777 Gregor et al June 7, 1960 2,940,841 Gregor et al June 14, 1960 4,381,188 Waizer et al Apr. 26, 1983 ______________________________________
Organically bonded grinding wheels are shown in these patents which include descriptions of the functioning of various kinds of grinding aids incorporated in such abrasive articles. Rainier suggests the use of sodium chloride in a heat hardenable resin bonded, abrasive article. This grinding aid or any one of several inorganic alkali or alkaline earth metal salts listed in his specification have been found to produce greater volume of metal removal for a given rate of wheel wear. These salts specifically identified by Rainier are: sodium chloride, sodium carbonate, potassium chloride, potassium carbonate, sodium sulphate, potassium sulphate, lithium sulphate, sodium pyrophosphate, potassium pyrophosphate, calcium chloride, calcium bromide, magnesium sulphate, barium chloride, barium bromide, magnesium chloride, magnesium bromide and strontium chloride.
Other grinding aids used with organic bonded abrasives are shown in Kistler who describes the use of a double salt of potassium calcium sulphate. Gregor et al U.S. Pat. No. 2,811,430 suggests the use of a physical mixture of salts with at least one selected from the group consisting of alkali metal salts of sulfuric, hydrochloric and hydrobromic acid together with zinc sulfide. Gregor et al in their U.S. Pat. No. 2,939,777 patent describe the use of these same alkali metal salts with lead sulfide, and in their U.S. Pat. No. 2,940,841 patent, with antimony sulfide. The first two Gregor et al patents state that the most effective physical mixtures of fillers either are at or near the amounts of each filler that would be the eutectic if the two salts were cofused.
Waizer et al is of general interest for the reason that his specification includes a discussion of the various types of fillers used in organically bonded abrasive articles and the purposes for which the respective types of fillers are used. The present invention is concerned with the Waizer et al type 3 "Active Fillers" that apparently undergo a chemical reaction or physical change as the grinding action proceeds that has a positive influence on the behavior of the abrasive during grinding.
It is conventional commercial practice to add combinations of grinding aids in organically bonded abrasive articles and various mixtures of alkali and alkaline metal chlorides, sulphates, sulphides have heretofore been used. It has been found that eutectic mixtures of such salts are preferred in organically bonded grinding wheels in order to improve the grinding ratio thereof.